1. Field of the Invention
The invention relates to a power transmission structure of a vehicle, and especially to a technology for restraining misalignment of axis between a first rotor and a second rotor connected with each other by spline-fitting, and for improving responsiveness of torque transmission between the first rotor and the second rotor.
2. Description of Related Art
A power transmission structure of a vehicle, which includes a first rotor and a second rotor, is known. The first rotor is connected with a power transmission member so as to be able to transmit power, the power transmission member transmitting power of an engine. The second rotor is provided concentrically with the first rotor and spline-fitted to the first rotor. FIG. 13 is a sectional view of an example of a power transmission structure 210 of a vehicle according to a related art. In the power transmission structure 210 of a vehicle, a first rotor 212 and a second rotor 214 are connected with each other by a spline fitting part 216 so as to be able to transmit power. In the spline fitting part 216, a spline tooth of the first rotor 212, to which, for example, power from an engine is transmitted through a power transmission member, and a spline tooth of the second rotor 214 provided concentrically with the first rotor 212, are spline-fitted to each other. Therefore, there is a possibility that tooth hitting sound occurs in the spline fitting part 216 due to misalignment of the axis of the first rotor 212 and the axis of the second rotor 214. The misalignment happens because of torque fluctuation and so on, transmitted through the first rotor 212, during an expansion stroke associated with ignition of the engine, especially when the rotational speed of the second rotor 214 is small.
In order to reduce the problem of the above-mentioned tooth hitting sound, a power transmission structure of a vehicle is proposed in, for example, Japanese Patent Application Publication No. 2011-214646 (JP 2011-214646 A), in which an annular elastic member that is elastically deformable in a radial direction is press-fitted between an inner peripheral surface and an outer peripheral surface of a first rotor and a second rotor, respectively adjacent to a spline fitting part in an axial direction. The inner peripheral surface and the outer peripheral surface of the first rotor and the second rotor face each other in the radial direction. Thus, misalignment between the axis of the first rotor and the axis of the second rotor is restrained, and tooth hitting sound generated in a spline fitting part caused by the axis misalignment is reduced.
In a vehicle in which the above-mentioned power transmission structure of a vehicle is provided, and, for example, the second rotor is connected with an electric motor, an damping control is performed. In the damping control, damping torque for restraining torsional vibration from an engine is outputted from the electric motor in order to, for example, restrain generation of cabin booming noise caused by torque fluctuation of, for example, an axle. Damping torque outputted in the damping control is outputted based on a phase of torsional vibration so as to cancel the torsional vibration. Therefore, it is required that no shift of the phase should happen when transmitting damping torque outputted from the electric motor to the power transmission member to which torsional vibration is transmitted through the second rotor. However, in the power transmission structure of a vehicle described in JP 2011-214646 A stated above, the elastic member, which is press-fitted between the second rotor connected with the electric motor, and the first rotor in the radial direction, has low rigidity. Since there is backlash in the spline fitting part between the first rotor and the second rotor, the elastic member is deformed in a circumferential direction between the second rotor and the first rotor, and responsiveness of torque transmission between the second rotor and the first rotor is deteriorated. This could cause a shift of the phase before and after transmission of damping torque of the electric motor from the second rotor to the first rotor. Due to the shift of the phase of the damping torque, a damping effect of torsional vibration of the engine by the damping control could be deteriorated.